1. Field of the Invention
This invention relates to a method for the disposal of a spent solid catalyst impregnated with an organic substance. More particularly, this invention relates to a method for the disposal of a solid catalyst, e.g. a spent ion-exchange resin, which comprises causing the solid catalyst for use in an apparatus for the production of an esterified compound to be washed as contained within the apparatus before it is discarded.
2. Description of the Related Art
The esterified compound is generally a compound produced by the reaction of an alcohol with a carboxylic acid. The (meth)acrylic ester, for example, which is a raw material for commercial production is produced in a large scale plant comprising a step for producing (meth)acrylic acid by the reaction of catalytic gas phase oxidation, a step for purifying the (meth)acrylic acid, and a step for esterifying the (meth)acrylic acid with an alcohol.
At the step for the reaction of esterification, the reactor for forming an esterified compound is generally packed with a solid catalyst such as an ion-exchange resin for catalyzing the reaction. The solid catalyst tends to be deteriorated by continuation of the reaction. When this solid catalyst has the activity thereof degraded to a certain level, it becomes necessary to withdraw the exhausted solid catalyst from the esterified compound forming reactor and replace it with a newly supplied solid catalyst. At present, it is customary for this withdrawal to be carried out by human power.
Since the amount of the catalyst in the esterified compound forming reactor is large and since the catalyst is contained in an impregnated state in the reaction solution, the effect of the reaction solution, for example, on the health of a worker engaging in the withdrawal has come to pose a problem.
This step for the production of an esterified compound will be specifically described below with reference to FIG. 1 which illustrates one example of the production of a (meth)acrylic ester by a procedure comprising a step of producing (meth)acrylic acid through the reaction of catalytic gas phase oxidation and a subsequent step of esterifying this acid. With reference to FIG. 1, {circle around (1)} stands for a (meth)acrylic acid extraction column, {circle around (2)} for a solvent separation column, {circle around (3)} for an esterification reactor, {circle around (4)} for a vaporizer, {circle around (5)} for a distillation column, {circle around (6)} for a thin-film vaporizer, {circle around (7)} for an oil-water separator, At for an alcohol stripper, {circle around (9)} for a light boiling substance separation column, {circle around (10)} for a high boiling substance separation column, 1 for an aqueous (meth)acrylic acid solution supply line, 2 for an extraction solvent supply line, 3 for a water phase emission line, 4 for a solvent phase supply line, 5 for a solvent fraction line, 6 for a crude (meth)acrylic acid supply line, 7 for an alcohol supply line, 8 for an esterification product supply line, 9 for a distilled fraction line, 10 for a high boiling substance supply line, 11 for a high boiling impurity extraction line, 12 for a recovered (meth)acrylic acid supply line, 13 for an alcohol-containing water phase supply line, 14 for a light boiling fraction line, 15 for a recovered alcohol extraction line, 16 for a waste water extraction line, 17 for a (meth)acrylic ester-containing oil phase supply line, 18 for a light boiling fraction line, 19 for an alcohol-containing water phase extraction line, 20 for a (meth)acrylic ester supply line, 21 for a (meth)acrylic ester product extraction line, and 22 for a high boiling substance extraction line.
First, the (meth)acrylic acid which is one of the raw materials for the production of an esterified compound is produced by the catalytic gas phase oxidation of propylene, acrolein, propane, isobutylene, methacrolein, etc. This reaction forms low boiling substances such as aldehyde, high boiling carboxylic acids such as terephthalic acid and benzoic acid, and such by-products of comparatively high boiling points as tarry substances besides the (meth)acrylic acid which is aimed at by the reaction. Thus, the gas containing the (meth)acrylic acid is sequestered with an absorbent such as water in an acrylic acid absorbing column (not shown) to obtain an aqueous (meth)acrylic acid solution and subsequently the aqueous (meth)acrylic acid solution is supplied via the line 1 to the (meth)acrylic acid extraction column {circle around (1)}. In the (meth)acrylic acid extraction column {circle around (1)}, the extraction solvent supplied through the line 2 and the aqueous (meth)acrylic acid solution are brought into counterflow contact with each other to induce extraction of the (meth)acrylic acid into a solvent phase. Then, the solvent phase containing the (meth)acrylic acid is supplied through the line 4 to the solvent separation column {circle around (2)} and the crude (meth)acrylic acid is extracted through the bottom of the solvent separation column {circle around (2)} and supplied through the line 6 to the esterification reactor {circle around (3)}.
The esterification reactor {circle around (3)} is filled with a strongly acidic cation exchange resin as a solid catalyst and is utilized for causing the (meth)acrylic acid supplied through the line 6 and the alcohol supplied through the line 7 to undergo a reaction for forming an esterified compound through the medium of the catalyst. The esterification reactor {circle around (3)}, therefore, is destined to contain the (meth)acrylic acid and the alcohol as the raw materials for the production of the esterified compound, the (meth)acrylic ester and water as the products of reaction, and the solid catalyst. During the normal operation of the apparatus, therefore, for the purpose of separating the (meth)acrylic acid, etc. contained in the esterification reactor {circle around (3)}, the reaction solution is supplied through the line 8 to the vaporizer {circle around (4)} the distilled therein and the (meth)acrylic ester, alcohol, and water are expelled by distillation through the top of the vaporizer {circle around (4)} and they are supplied through the line 9 to the oil-water separator {circle around (7)}. The oil phase containing the (meth)acrylic ester separated in the oil-water separator {circle around (7)} is supplied through the line 17 to the light boiling substance separation column {circle around (9)} and distilled therein and the (meth)acrylic ester is extracted through the bottom of the light boiling substance separation column {circle around (9)} and supplied through the line 20 to the high boiling substance separation column {circle around (10)}. In this separation column {circle around (10)}, the (meth)acrylic ester is rectified and the (meth)acrylic ester as a finished product is obtained through the line 21. Incidentally, the water phase which has been separated in the oil-water separator {circle around (7)} is supplied, for the purpose of recovering the alcohol contained therein, to the alcohol stripper {circle around (8)} and the alcohol is expelled by distillation through the top of the stripper and recovered from the line 15.
When the solid catalyst which is packed in the esterification reactor {circle around (3)} is deteriorated by use and is discarded as mentioned above, it has been customary to effect the extraction of the deteriorated solid catalyst from the reactor by human power. The chemical stimulation from the raw materials for reaction, the product of the reaction, and the by-products and the physical obstruction such as adhesion of polymer compel the operator engaging in the work of discarding the spent solid catalyst to experience spiritual displeasure and arouse anxiety about possible infliction of an adverse effect on the operator""s health. Further, in terms of safety, the solvent contained in the reaction solution entails the problem of threatening ignition. The disposal of the spent solid catalyst by human power is generally difficult, with the largeness of the volume of the esterification reactor {circle around (3)} itself as a contributory factor.
More often than not, an ion-exchange resin is used as the solid catalyst which fills the esterification reactor {circle around (3)}, a main component of the apparatus for the production of the esterified compound, no matter whether the solid catalyst is used in a fixed-bed pattern or in a fluidized-bed pattern. The ion-exchange resin is a catalyst easy to deteriorate and, therefore, the esterification reactor {circle around (3)} using this ion-exchange resin frequently needs to undergo an operation of disposal. In a large scale plant, however, the stop and the start of an operation require enormous labor and time and even partial stop of a component device necessitates adjustment of a series of relevant reaction conditions. When the stop of the esterification reactor results in degrading the productivity of the esterified compound aimed at by the operation, the object of attaining quantity production is crushed. Since the spent solid catalyst must be, therefore, discarded and replaced with a new supply quickly, the desirability of adopting the most efficient method for the disposal has been finding growing recognition. The term xe2x80x9cfixed-bed patternxe2x80x9d refers to a method for performing a given reaction in an esterification reactor packed with a solid catalyst such as a strongly acidic cation-exchange resin in a fixed pattern and the term xe2x80x9cfluidized-bed patternxe2x80x9d refers to a method for effecting a reaction of esterification by suspending and dispersing a solid catalyst like the fashion of the so-called fluidized bed, i.e. introducing a gas either with a stirring device or through the bottom part of an esterification reactor make an ion-exchange resin suspend and disperse in a reaction solution and the water formed by the reaction of esterification in the reaction solution is expelled by azeotropic distillation. The reaction solution which contains the ion-exchange resin is treated with a catalyst separation device such as a filter to effect separation of the ion-exchange resin and the reaction solution.
When the esterified compound happens to use such a reacting monomer as (meth)acrylic acid as one of the raw materials for the production thereof, the polymer of (meth)acrylic acid, the polymer of a (meth)acrylic ester, etc. possibly adhere to or accumulate on the solid catalyst to be discarded. The removal of these polymers which also adhere to the esterification reactor necessitates use of a washing solvent in a large volume. When the cleaning fluid thus used for the removal is discarded or disposed of as by combustion, the disposal entails generation of carbon dioxide and pollution of rivers and coasts with an organic solvent and results in violating environmental protection. Thus,the desirability of developing a means which is capable of disposing of the spent cleaning fluid with due consideration to the environmental protection has been finding public approval.
The present inventor, after studying in detail the process for the production of an esterified compound, has discovered that when water or a specific solvent is added to the esterification reactor and used therein for washing a spent solid catalyst contained in the reactor, an operator engaging in the work of extracting the solid catalyst from the esterification reactor is enabled to avoid experiencing displeasure and the useful substances contained in the cleaning fluid is enabled to be reused by using the cleaning fluid for distillation in a device operated in the apparatus for the production of the esterified compound. This invention has been perfected as a result. To be specific, the task imposed on this invention is accomplished by the following Item (1).
(1) A method for the disposal of a spent solid catalyst in an apparatus for the production of an esterified compound comprising an esterification reactor provided with a part packed with a solid catalyst and a distillation part, which method is characterized by washing the spent solid catalyst in the part packed with the solid catalyst with water and/or a component of the raw material for an esterifid substance.
According to this invention, the existing apparatus to be used in the process for production of an esterified compound can be operated in its unaltered form, the water by-produced in the reaction of esterification and the alcohol as a raw material for the esterification can be used as the cleaning fluid, and such effective components can be recovered from the cleaning fluid. Thus,the stimulation from the offensive odor and the volatile component which have heretofore posed a problem to the removal of the spent solid catalyst is eliminated and the safety in terms of health and in terms of operation is secured. Where a plurality of such esterification reactor are parallelly connected, the practice of discarding only the solid catalyst in part of these esterified compound generators brings the particular efficiency of enabling the disposal to be effected while retaining the existing working apparatus in continued operation.